Our overall objective is to understand some of the events that occur during the processes of cessation of cellular proliferation, senscence and terminal differentiation, and how those processes might relate to one another. We hypothesize that these processes occur through changes of the programming of gene expression at the nuclear level. While some alterations of nuclear events have been documented, we propose to explore the metabolism, distribution and behavior of a unique class of nuclear constituents for possible insights into the programming. We will examine synthetic, degradative, and distributive patterns of small nuclear RNA's (snRNA's) within the nuclei of Friend erythroleukemic cells, and rat myoblasts (as models of differentiation), and human diploid fibroblasts (as a model for cellular senescence) in an effort to correlate these patterns with defined changes in nuclear activity. We will then attempt to use this information to determine whether cessation of proliferation, senescence, and terminal differentiation arise by similar or different processes and how they may interact.